1. Field of the Invention
The invention relates to a method for time synchronization in a communication network, and to a corresponding communication network.
2. Description of the Related Art
In many technical applications of communication networks it is necessary to temporally synchronize the network nodes participating in the communication, such that all the network nodes provide exactly synchronous time information. In particular, within industrial automation installations, it is particularly important that the automatic work operations of different network nodes be accurately temporally coordinated with one another.
Various standards for time synchronization in communication networks, are known from the prior art, e.g., Institute of Electrical and Electronic Engineer (IEEE) standard 1588, IEEE standard 802.1AS and International Electrotechnical Commission (IEC) standard 61158. In this case, the time information of a master node, which detects the time with a master clock, is communicated to all the other subscribers in the communication network, which constitute slave nodes. The time information is contained in synchronization messages that are forwarded by the salve nodes. Upon forwarding, the slave nodes add all propagation time delays known to them to the content of the synchronization message. In this way, a slave node can synchronize its slave time, which it detects with an internal clock, with the master time based on the content of the synchronization messages.
In the known standards, each node adds to corresponding fields of the synchronization message firstly an internal processing time (a Bridge Delay) and secondly a transmission time (a Line Delay). The internal processing time specifies the time duration required by a node for processing the messages between reception and re-emission. By contrast, the transmission time defines the time period between the emission of the message at the preceding network node and the reception at the processing network node. This transmission time is conventionally estimated by separate exchange of messages between neighboring network nodes, which is associated with additional complexity and leads to estimation errors.